1. Technical Field
The invention is related to skip-field video cassette recorders in which the required tape speed is reduced by a factor of two for a given signal bandwidth.
2. Description of Related Art
U.S. patent application Ser. No. 908,750, filed Sept. 18, 1986 by Hans-Peter Baumeister et al. and entitled "ZERO GUARD-BAND SKIP-FIELD VIDEO CASSETTE RECORDER" describes (among other things) a skip-field video recorder in which the missing fields in the playback signal are filled in by playing each field twice during playback. Various related signal processing techniques are known in the art, for averaging, interpolating or repeating video signals, as disclosed in U.S. Pat. Nos. 4,298,896; 4,393,414; 3,886,589; 4,348,689; 3,470,315; and 3,944,728.
Skip-field video recording is plagued by the limitation that the vertical resolution of a playback skip-field video signal is significantly reduced. This is because the "skipped" fields must be filled in by repeating or interpolating previously recorded video fields. If only even video fields, for example, are recorded, then the information in the horizontal video lines of the odd video fields is permanently lost, thus reducing the vertical image resolution (number of horizontal video lines) by a factor of two. Simply repeating a video field twice during playback to fill in for a skipped field does not recover the lost information and therefore does not really improve the vertical resolution. Even the technique of interpolating between adjacent horizontal lines of a given video field does not really provide the "missing" information of the skipped field. Apparently, no practical technique is known for achieving full vertical resolution in a skip-field video recorder. It is an object of the present invention to overcome this limitation.